1. Field of the Invention
This invention generally relates to concrete reclamation, and more particularly to methods and systems for reclaiming in a closed system unpoured concrete and other material which would normally be discarded so that no unused products are generated.
2. Background Art
Concrete reclamation is fast becoming a standard in the concrete production and construction industries. The advantages of reclaiming unneeded or unused concrete at the end of a concrete pouring cycle are clear from both an economic and an environmental position.
Various attempts in the industry providing for concrete reclamation have been described and used in the field. The following U.S. Patents are examples of these attempts: U.S. Pat. Nos. 2,942,731, No. 3,278,022, No. 3,596,759, No. 3,695,427, No. 3,997,434 and No. 4,488,815. These patents are mostly concerned with the reclamation of small quantities of concrete which remain in a "ready-mix" truck after the concrete in the truck has been discharged. The most common method disclosed by these patents is the reclamation of the slurry water, which contains small amounts of dissolved concrete, and which results when a truck or mixer has been flushed with water to clean out the mixing chamber. The majority of these patents are concerned with the separation of the cement slurry into its water, sand and gravel constituents.
As often happens at a building site, however, and especially at the end of a concrete pouring job, a substantial quantity of concrete will be unused because there is no need to pour it at the job site. The amount may vary depending on the accuracy of the projections of concrete which are needed at a job site. Because the concrete is first mixed at a mixing plant and transported by a ready mix truck to a job site, the projected need for concrete will usually exceed the amount which is actually used to avoid the necessity of extra trips. The usual eventuality is the return of the ready mix truck at the end of the day with a substantial portion of the unpoured concrete still in the ready-mix truck. Thus, there is a need in the industry for a method of and system for reclaiming the unused portion of the concrete for future use.
One problem which results from storage of concrete for use during the next day's concrete pour is that concrete left standing for a sufficient length of time will hydrate and set in position. Concrete which has set cannot be used for pouring and cannot be recycled in the normal course. Various method for retarding hydration of concrete have been proposed in the prior art, one of which is disclosed by U.S. Pat. No. 4,964,917, which is incorporated by reference herein. That patent is directed to a method and composition for retarding hydration of concrete and for reversal of the process, i.e. for acceleration of concrete hydration, when the concrete is again desired for pouring.
Even when armed with the teachings of U.S. Pat. No. 4,964,917, however, there remains the problem of bulk material handling at the ready-mix plant, especially during times of high return volume of unpoured and unused concrete, such as at the end of the day, when several trucks may be waiting to discharge excess concrete from their respective mixers.